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Commit cc2d5863 authored by Taehee Yoo's avatar Taehee Yoo Committed by Pablo Neira Ayuso
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netfilter: nf_nat_snmp_basic: use asn1 decoder library 



The basic SNMP ALG parse snmp ASN.1 payload
however, since 2012 linux kernel provide ASN.1 decoder library.
If we use ASN.1 decoder in the /lib/asn1_decoder.c, we can remove
about 1000 line of ASN.1 parsing routine.

To use asn1_decoder.c, we should write mib file(nf_nat_snmp_basic.asn1)
then /script/asn1_compiler.c makes *-asn1.c and *-asn1.h file
at the compiletime.(nf_nat_snmp_basic-asn1.c, nf_nat_snmp_basic-asn1.h)
The nf_nat_snmp_basic.asn1 is made by RFC1155, RFC1157, RFC1902, RFC1905,
RFC2578, RFC3416. of course that mib file supports only the basic SNMP ALG.

Previous SNMP ALG mangles only first octet of IPv4 address.
but after this patch, the SNMP ALG mangles whole IPv4 Address.
And SNMPv3 is not supported.

I tested with snmp commands such ans snmpd, snmpwalk, snmptrap.

Signed-off-by: default avatarTaehee Yoo <ap420073@gmail.com>
Signed-off-by: default avatarPablo Neira Ayuso <pablo@netfilter.org>
parent bea588b0

net/ipv4/netfilter/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -158,6 +158,7 @@ config NF_NAT_SNMP_BASIC 
	depends on NF_CONNTRACK_SNMP

	depends on NETFILTER_ADVANCED

	default NF_NAT && NF_CONNTRACK_SNMP

	select ASN1

	---help---



	  This module implements an Application Layer Gateway (ALG) for

net/ipv4/netfilter/Makefile

+6 −0
Original line number Diff line number Diff line
@@ -27,9 +27,15 @@ obj-$(CONFIG_NF_REJECT_IPV4) += nf_reject_ipv4.o 
# NAT helpers (nf_conntrack)

obj-$(CONFIG_NF_NAT_H323) += nf_nat_h323.o

obj-$(CONFIG_NF_NAT_PPTP) += nf_nat_pptp.o



nf_nat_snmp_basic-y := nf_nat_snmp_basic-asn1.o nf_nat_snmp_basic_main.o

nf_nat_snmp_basic-y : nf_nat_snmp_basic-asn1.h nf_nat_snmp_basic-asn1.c

obj-$(CONFIG_NF_NAT_SNMP_BASIC) += nf_nat_snmp_basic.o

clean-files := nf_nat_snmp_basic-asn1.c nf_nat_snmp_basic-asn1.h



obj-$(CONFIG_NF_NAT_MASQUERADE_IPV4) += nf_nat_masquerade_ipv4.o





# NAT protocols (nf_nat)

obj-$(CONFIG_NF_NAT_PROTO_GRE) += nf_nat_proto_gre.o

net/ipv4/netfilter/nf_nat_snmp_basic.asn1

0 → 100644
+177 −0
Original line number Diff line number Diff line 
Message ::=

	SEQUENCE {

		version

			INTEGER ({snmp_version}),



		community

			OCTET STRING,



		pdu

			PDUs

	}





ObjectName ::=

	OBJECT IDENTIFIER



ObjectSyntax ::=

	CHOICE {

		simple

			SimpleSyntax,



		application-wide

			ApplicationSyntax

	}



SimpleSyntax ::=

	CHOICE {

		integer-value

			INTEGER,



		string-value

			OCTET STRING,



		objectID-value

			OBJECT IDENTIFIER

	}



ApplicationSyntax ::=

	CHOICE {

		ipAddress-value

			IpAddress,



		counter-value

			Counter32,



		timeticks-value

			TimeTicks,



		arbitrary-value

			Opaque,



		big-counter-value

			Counter64,



		unsigned-integer-value

			Unsigned32

	}



IpAddress ::=

	[APPLICATION 0]

		IMPLICIT OCTET STRING OPTIONAL ({snmp_helper})



Counter32 ::=

	[APPLICATION 1]

		IMPLICIT INTEGER OPTIONAL



Unsigned32 ::=

	[APPLICATION 2]

		IMPLICIT INTEGER OPTIONAL



Gauge32 ::= Unsigned32 OPTIONAL



TimeTicks ::=

	[APPLICATION 3]

		IMPLICIT INTEGER OPTIONAL



Opaque ::=

	[APPLICATION 4]

		IMPLICIT OCTET STRING OPTIONAL



Counter64 ::=

	[APPLICATION 6]

		IMPLICIT INTEGER OPTIONAL



PDUs ::=

	CHOICE {

		get-request

			GetRequest-PDU,



		get-next-request

			GetNextRequest-PDU,



		get-bulk-request

			GetBulkRequest-PDU,



		response

			Response-PDU,



		set-request

			SetRequest-PDU,



		inform-request

			InformRequest-PDU,



		snmpV2-trap

			SNMPv2-Trap-PDU,



		report

			Report-PDU

	}



GetRequest-PDU ::=

	[0] IMPLICIT PDU OPTIONAL



GetNextRequest-PDU ::=

	[1] IMPLICIT PDU OPTIONAL



Response-PDU ::=

	[2] IMPLICIT PDU OPTIONAL



SetRequest-PDU ::=

	[3] IMPLICIT PDU OPTIONAL



-- [4] is obsolete



GetBulkRequest-PDU ::=

	[5] IMPLICIT PDU OPTIONAL



InformRequest-PDU ::=

	[6] IMPLICIT PDU OPTIONAL



SNMPv2-Trap-PDU ::=

	[7] IMPLICIT PDU OPTIONAL



Report-PDU ::=

	[8] IMPLICIT PDU OPTIONAL



PDU ::=

	SEQUENCE {

		request-id

			INTEGER,



		error-status

			INTEGER,



		error-index

			INTEGER,



		variable-bindings

			VarBindList

	}





VarBind ::=

	SEQUENCE {

		name

			ObjectName,



	CHOICE {

		value

			ObjectSyntax,



		unSpecified

			NULL,



		noSuchObject

			[0] IMPLICIT NULL,



		noSuchInstance

			[1] IMPLICIT NULL,



		endOfMibView

			[2] IMPLICIT NULL

	}

}



VarBindList ::= SEQUENCE OF VarBind

net/ipv4/netfilter/nf_nat_snmp_basic.c

deleted100644 → 0
+0 −1192

File deleted.

Preview size limit exceeded, changes collapsed.

net/ipv4/netfilter/nf_nat_snmp_basic_main.c

0 → 100644
+235 −0
Original line number Diff line number Diff line 
/*

 * nf_nat_snmp_basic.c

 *

 * Basic SNMP Application Layer Gateway

 *

 * This IP NAT module is intended for use with SNMP network

 * discovery and monitoring applications where target networks use

 * conflicting private address realms.

 *

 * Static NAT is used to remap the networks from the view of the network

 * management system at the IP layer, and this module remaps some application

 * layer addresses to match.

 *

 * The simplest form of ALG is performed, where only tagged IP addresses

 * are modified.  The module does not need to be MIB aware and only scans

 * messages at the ASN.1/BER level.

 *

 * Currently, only SNMPv1 and SNMPv2 are supported.

 *

 * More information on ALG and associated issues can be found in

 * RFC 2962

 *

 * The ASB.1/BER parsing code is derived from the gxsnmp package by Gregory

 * McLean & Jochen Friedrich, stripped down for use in the kernel.

 *

 * Copyright (c) 2000 RP Internet (www.rpi.net.au).

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation; either version 2 of the License, or

 * (at your option) any later version.

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, see <http://www.gnu.org/licenses/>.

 *

 * Author: James Morris <jmorris@intercode.com.au>

 *

 * Copyright (c) 2006-2010 Patrick McHardy <kaber@trash.net>

 */

#include <linux/module.h>

#include <linux/moduleparam.h>

#include <linux/types.h>

#include <linux/kernel.h>

#include <linux/in.h>

#include <linux/ip.h>

#include <linux/udp.h>

#include <net/checksum.h>

#include <net/udp.h>



#include <net/netfilter/nf_nat.h>

#include <net/netfilter/nf_conntrack_expect.h>

#include <net/netfilter/nf_conntrack_helper.h>

#include <linux/netfilter/nf_conntrack_snmp.h>

#include "nf_nat_snmp_basic-asn1.h"



MODULE_LICENSE("GPL");

MODULE_AUTHOR("James Morris <jmorris@intercode.com.au>");

MODULE_DESCRIPTION("Basic SNMP Application Layer Gateway");

MODULE_ALIAS("ip_nat_snmp_basic");



#define SNMP_PORT 161

#define SNMP_TRAP_PORT 162



static DEFINE_SPINLOCK(snmp_lock);



struct snmp_ctx {

	unsigned char *begin;

	__sum16 *check;

	__be32 from;

	__be32 to;

};



static void fast_csum(struct snmp_ctx *ctx, unsigned char offset)

{

	unsigned char s[12] = {0,};

	int size;



	if (offset & 1) {

		memcpy(&s[1], &ctx->from, 4);

		memcpy(&s[7], &ctx->to, 4);

		s[0] = ~0;

		s[1] = ~s[1];

		s[2] = ~s[2];

		s[3] = ~s[3];

		s[4] = ~s[4];

		s[5] = ~0;

		size = 12;

	} else {

		memcpy(&s[0], &ctx->from, 4);

		memcpy(&s[4], &ctx->to, 4);

		s[0] = ~s[0];

		s[1] = ~s[1];

		s[2] = ~s[2];

		s[3] = ~s[3];

		size = 8;

	}

	*ctx->check = csum_fold(csum_partial(s, size,

					     ~csum_unfold(*ctx->check)));

}



int snmp_version(void *context, size_t hdrlen, unsigned char tag,

		 const void *data, size_t datalen)

{

	if (*(unsigned char *)data > 1)

		return -ENOTSUPP;

	return 1;

}



int snmp_helper(void *context, size_t hdrlen, unsigned char tag,

		const void *data, size_t datalen)

{

	struct snmp_ctx *ctx = (struct snmp_ctx *)context;

	__be32 *pdata = (__be32 *)data;



	if (*pdata == ctx->from) {

		pr_debug("%s: %pI4 to %pI4\n", __func__,

			 (void *)&ctx->from, (void *)&ctx->to);



		if (*ctx->check)

			fast_csum(ctx, (unsigned char *)data - ctx->begin);

		*pdata = ctx->to;

	}



	return 1;

}



static int snmp_translate(struct nf_conn *ct, int dir, struct sk_buff *skb)

{

	struct iphdr *iph = ip_hdr(skb);

	struct udphdr *udph = (struct udphdr *)((__be32 *)iph + iph->ihl);

	u16 datalen = ntohs(udph->len) - sizeof(struct udphdr);

	char *data = (unsigned char *)udph + sizeof(struct udphdr);

	struct snmp_ctx ctx;

	int ret;



	if (dir == IP_CT_DIR_ORIGINAL) {

		ctx.from = ct->tuplehash[dir].tuple.src.u3.ip;

		ctx.to = ct->tuplehash[!dir].tuple.dst.u3.ip;

	} else {

		ctx.from = ct->tuplehash[!dir].tuple.src.u3.ip;

		ctx.to = ct->tuplehash[dir].tuple.dst.u3.ip;

	}



	if (ctx.from == ctx.to)

		return NF_ACCEPT;



	ctx.begin = (unsigned char *)udph + sizeof(struct udphdr);

	ctx.check = &udph->check;

	ret = asn1_ber_decoder(&nf_nat_snmp_basic_decoder, &ctx, data, datalen);

	if (ret < 0) {

		nf_ct_helper_log(skb, ct, "parser failed\n");

		return NF_DROP;

	}



	return NF_ACCEPT;

}



/* We don't actually set up expectations, just adjust internal IP

 * addresses if this is being NATted

 */

static int help(struct sk_buff *skb, unsigned int protoff,

		struct nf_conn *ct,

		enum ip_conntrack_info ctinfo)

{

	int dir = CTINFO2DIR(ctinfo);

	unsigned int ret;

	const struct iphdr *iph = ip_hdr(skb);

	const struct udphdr *udph = (struct udphdr *)((__be32 *)iph + iph->ihl);



	/* SNMP replies and originating SNMP traps get mangled */

	if (udph->source == htons(SNMP_PORT) && dir != IP_CT_DIR_REPLY)

		return NF_ACCEPT;

	if (udph->dest == htons(SNMP_TRAP_PORT) && dir != IP_CT_DIR_ORIGINAL)

		return NF_ACCEPT;



	/* No NAT? */

	if (!(ct->status & IPS_NAT_MASK))

		return NF_ACCEPT;



	/* Make sure the packet length is ok.  So far, we were only guaranteed

	 * to have a valid length IP header plus 8 bytes, which means we have

	 * enough room for a UDP header.  Just verify the UDP length field so we

	 * can mess around with the payload.

	 */

	if (ntohs(udph->len) != skb->len - (iph->ihl << 2)) {

		nf_ct_helper_log(skb, ct, "dropping malformed packet\n");

		return NF_DROP;

	}



	if (!skb_make_writable(skb, skb->len)) {

		nf_ct_helper_log(skb, ct, "cannot mangle packet");

		return NF_DROP;

	}



	spin_lock_bh(&snmp_lock);

	ret = snmp_translate(ct, dir, skb);

	spin_unlock_bh(&snmp_lock);

	return ret;

}



static const struct nf_conntrack_expect_policy snmp_exp_policy = {

	.max_expected	= 0,

	.timeout	= 180,

};



static struct nf_conntrack_helper snmp_trap_helper __read_mostly = {

	.me			= THIS_MODULE,

	.help			= help,

	.expect_policy		= &snmp_exp_policy,

	.name			= "snmp_trap",

	.tuple.src.l3num	= AF_INET,

	.tuple.src.u.udp.port	= cpu_to_be16(SNMP_TRAP_PORT),

	.tuple.dst.protonum	= IPPROTO_UDP,

};



static int __init nf_nat_snmp_basic_init(void)

{

	BUG_ON(nf_nat_snmp_hook != NULL);

	RCU_INIT_POINTER(nf_nat_snmp_hook, help);



	return nf_conntrack_helper_register(&snmp_trap_helper);

}



static void __exit nf_nat_snmp_basic_fini(void)

{

	RCU_INIT_POINTER(nf_nat_snmp_hook, NULL);

	synchronize_rcu();

	nf_conntrack_helper_unregister(&snmp_trap_helper);

}



module_init(nf_nat_snmp_basic_init);

module_exit(nf_nat_snmp_basic_fini);